1. Field of the Invention
The present invention relates to a small-scale linear actuator for exemplary use in a process for component mounting and measuring or the like, such as a process for mounting and measuring a chip component using a probe.
2. Description of the Related Art
Generally, a linear actuator comprises a fixed element and a moving element. For instance, the fixed element can comprise a yoke and a magnet, and the moving element can comprise a bobbin and an electromagnetic coil. When current is injected into the coil, the action of the magnetic field and the current produces thrust on the moving element. As a result, the moving element moves in the direction of the thrust while maintaining a very small gap between the moving element and the fixed element. When the direction of current flow is reversed, the thrust is reversed. By using a lightweight moving element and appropriately controlling the electrical current, it is possible to achieve excellent responsiveness and precise position control.
It is preferable that the acting force (thrust) of the actuator to an outside is constant within a movable stroke area in case of a mounting process or an inspection process. However, in the configuration described above, the magnetic flux acting on the coil varies depending on the position of the moving element, and consequently, the resultant force acting on the actuator also varies within the stroke range.
In order to make the thrust of the actuator constant, the length of the magnet in the stroke direction may be lengthened so that the coil can move within a constant magnetic flux area of the magnet. However, in this structure, when power is switched off due to an emergency shutdown or the like, thrust is lost and the moving element stops in a position other than the desired position. In particular, when the linear actuator is used as a Z-axis actuator in the process of mounting and measuring or the like, there is a possibility that a dead load will cause the moving element to drop below the lower limit of the stroke, thereby causing damage to the device or product, or causing injury to the operator. Thus, the fact that the actuator stops in a position not intended by the designer gives rise to problems of safety and product quality.
Furthermore, when the actuator remains stationary in one place for a long time due to malfunction or while waiting for items to be processed, heat is generated in the actuator, leading to problems of poor performance and shortened life span.